fix rtmp-stream stalling execution

Run rtmp-stream.sh in the background, preventing wz_user.sh from completing execution

SD_ROOT/wz_mini/etc/init.d/wz_user.sh

@@ -674,7 +674,7 @@ if ([[ "$RTSP_LOW_RES_ENABLED" == "true" ]] || [[ "$RTSP_HI_RES_ENABLED" == "tru
 	echo "delay RTMP server"
 	#Follow the delay from the RTSP server
 	sleep 5
-	/opt/wz_mini/bin/rtmp-stream.sh "$RMTP_STREAM_SERVICE" "$RTMP_AUDIO"
+	/opt/wz_mini/bin/rtmp-stream.sh "$RMTP_STREAM_SERVICE" "$RTMP_AUDIO" &
 fi
 
 if [[ "$NIGHT_DROP_DISABLE" == "true" ]]; then